EFFECT OF SINTERING ATMOSPHERE ON THE DENSIFICATION OF UO2-GD2O3 COMPACTS

Sintering kinetics of powder compacts of UO2-(5, 10 wt%)Gd2O3 and UO2 have been studied in controlled atmospheres of H2O/H-2 and CO2/CO mixed gases by using a dilatometer. The densification rates and microstructure of the sintered pellets are considerably influenced by both the sintering atmosphere and Gd2O3 content. After a heat treatment of 1650-degrees-C for 2 h, the sintered densities for UO2-Gd2O3 pellets begin to decrease above the threshold oxidizing atmospheres, while the density for the UO2 pellet increases slightly with more oxidizing atmospheres. These behaviors result from the difference in development of pore structure during sintering: the pore structure of UO2-Gd2O3 pellets varies from an open pore structure to a closed pore structure on changing the sintering atmosphere from reducing to oxidizing. On the other hand, the pore structure of the UO2 pellet is hardly affected by the sintering atmosphere. The formation of (U,Gd)O2 solid solutions and the grain growth are enhanced with more oxidizing atmospheres.